The present invention is directed to the preparation of high molecular weight hyperbranched polyester and polyamide polymers. The polymers are produced by a one-step process which entails polymerizing specific monomers of the formula A--R--B.sub.2 in such a manner that side-reactions, i.e. reverse reactions, isomerization, crosslinking, and the like are substantially avoided.
P. J. Flory, J. Am. Chem. Soc., 74, 2718 (1952) and Principles of Polymer Chemistry, Cornell University Press, 1953, pp. 361-70, discusses the theory of condensation polymerization of so-called AB.sub.n -type monomers wherein A and B functions condense together to form branched polymers. While theoretically such polymers should be of high molecular weight, such has not been the case in actual practice. The only specific disclosures of such polymers are obtained by (i) the Friedel-Crafts condensation of benzyl halides in the presence of a MX.sub.3 catalyst wherein X is a halogen, (ii) the elimination metal halides from alkali metal salts of trihalophenols, and (iii) intermolecular etherification of D-glucose in the presence of dilute acids to form a soluble polyglucose. Hyperbranched polyester and polyamide polymers are not disclosed. Also, only low molecular weight polymers, i.e. less than about 1,000 daltons, were obtained.
A recent attempt at producing a poly(arylene)polymer by following Flory's theory has also resulted in a polymer having a number average molecular weight below 10,000. Kim et al., J. Am. Chem. Soc., 1990, 112, 4592-3, and Kim U.S. Pat. No. 4,857,630 disclose wholly aromatic poly(arylene) polymers prepared by the homocoupling of (3,5-dibromophenyl) boronic acid in a mixture of an organic solvent and aqueous sodium carbonate along with a palladium-containing catalyst. The molecular weight of the polymer was found to depend on the organic solvent and temperature employed during polymerization and addition of additional monomer at the end of the polymerization neither increased the molecular weight nor gave a bimodal distribution. Kim et al. could not explain what causes the molecular growth of the system to stop. Only low molecular weight polymers, i.e. about 5,000 daltons, were produced. During the polymerization, only single bonds between arylene groups are formed and no polyester or polyamide polymers are disclosed or suggested.
Baker et al. U.S. Pat. No. 3,669,939 discloses condensation polymerizing other ARB.sub.2 monomers, i.e. polyhydroxymonocarboxylic acid aliphatic compounds, but only succeeds in generating polymers with molecular weights below 4,000 daltons. While the molecular weights obtained in Baker et al. are not provided, the acid values which are provided permit the calculation thereof.
In view of the previous inability to directly prepare high molecular weight hyperbranched polymers in accordance with Flory's theory, the art is replete with multi-step procedures attempting to accomplish a similar result. For instance, Tomalia et al. U.S. Pat. Nos. 4,507,466, 4,558,120, 4,568,737, 4,587,329, and 4,737,558 disclose dense "starburst" polymers produced by allowing a polyfunctional amide core molecule to react with excess methyl acrylate in a Michel-type addition. Each arm of the resulting star-branched molecule is then reactivated to an amine-terminated moiety by exhaustive amidation using excess 1,2-diaminoethane to afford a chain extended product in which each primary amino group becomes a new branch point in the next series of Michael additions. The polymers are thus built up, layer after layer, from a core substance by selective condensation of functional groups with each successive layer becoming a core for the subsequent layer. Only aliphatic polyamides and polyethers are exemplified and the monomers used are of the A-B type.
Similarly, Denkewalter et al. U.S. Pat. Nos. 4,289,872, 4,360,646 and 4,410,688 disclose highly branched polyamide polymers produced from lysine--an A--R--B.sub.2 monomer having one carboxy group, two amino groups, and an aliphatic body--but utilizes a multi-step process of blocking the functional groups and then unblocking them. only relatively low molecular weight polymers were produced due to the inherent difficulty in obtaining complete reaction for each of the multiple of blocking, unblocking, and reacting steps.
Copending application U.S. Ser. No. 07/369,270, filed Jun. 21, 1989, now U.S. Pat. No. 5,041,516, issued Aug. 20, 1991, of Frechet et al. discloses a convergent pathway for preparing dendritic molecules in which accurate placement of one or more functional groups on the outer surface of the macromolecules is accomplished. The convergent approach entails building the final molecule by beginning at its periphery, rather than at its core as in divergent procedures, but still requires a blocking-unblocking multi-step operation, albeit of only a single reactive group at a single focal point which avoids the prior art problem of dealing with a multiplicity of reactive groups as the molecule grows.
Extensive prior art exists on the preparation of linear aromatic polyesters derived from, for example, 4-hydroquinone and phthalic acid or derivatives thereof. Also, Kricheldorf et al., Polymer Bulletin 1, 383-388 (1979) discloses preparing linear aromatic polyesters by heating trimethylsilyloxybenzoyl chloride to greater than 150.degree. C. Kricheldorf et al., Polymer, 23, 1821-29 (1982) discloses forming predominantly aromatic polyesters from 3-trimethylsilyloxybenzoyl chloride and incorporating small amounts, i.e. 0.6 to 16.6 mole %, of 3,5-bis(trimethylsilyloxy)benzoyl chloride to produce a few branch points. The polyesters so formed behave as predominantly linear polymers since they contain only a few potential branches while the present high molecular weight hyperbranched polyesters behave much more like individual particles.
Accordingly, the art has failed to teach a method which succeeds in producing high molecular weight hyperbranched aromatic polyester and polyamide polymers and it is an object of the present invention to produce such polymers to take advantage of their unique properties, i.e. of high polarity, low crystallinity, and lower than usual viscosity.